Background: Overuse of health services whose immediate or downstream costs or harms exceed their benefits (i.e., low-value health services) is a major driver of healthcare costs in the United States. Comprehensive measures of low-value service use have been applied to identify low-value services with the highest utilization and costs in non-VA populations, but less is known about which low-value services are most frequently used and costly in Veterans managed in the Veterans Health Administration (VHA). Also, all Veterans aged 65+ are eligible to use non-VA care via Medicare, and Veterans of all ages increasingly receive care outside VA through VA Community Care (VACC). Past research suggests that dual use of VA and non- VA care places Veterans at risk for overuse of health services, but information on Veterans? use of low-value services in non-VA settings is lacking. Significance/Impact: Our objective is to determine the extent of utilization, costs, and determinants of Veterans' low-value service use within and outside VA. Our study will identify the low-value services most commonly used by Veterans through VA Medical Centers (VAMCs), VACC, and dual Medicare benefits, and those that are most costly. This study will inform policies and interventions, including possible new quality metrics, to reduce low-value care provided to Veterans. Results will be valuable to our VA partners (Office of Reporting, Analysis, Performance Improvement and Deployment, and Office of Community Care) who are committed to ensuring that Veterans receive high-value services regardless of where they receive care. It will also empower Veterans to consider value of care when choosing between a VA vs non-VA setting. This study addresses two Veteran Care Priorities (health care value; quality/ safety of care) and the VA legislation priority to understand impact of non-VA care on value of care received by Veterans in light of the MISSION Act. Innovation: Current VA performance metrics capture key dimensions of access, quality, safety, and efficiency, but do not address Veterans' receipt of low-value care or quality of care received in non-VA settings. Our project will use novel methods to quantify use and determinants of an array of low-value services that Veterans may receive both within and outside of VA. Specific Aims: Aim 1: Quantify utilization and costs of low-value services provided to VHA enrollees in VAMCs and VACC, and characterize variation across VA facilities in low-value services provided in each setting. Aim 2: Quantify utilization and costs of low-value services used by dual VHA-Medicare enrollees in VAMCs and non-VA settings through Medicare, and characterize VA facility-level variation in low-value services provided in each setting. Aim 3: Identify barriers and facilitators of de-implementing low-value services in each setting. Methodology: In Aim 1, we will apply a claims-based measure of low-value care to VA utilization data and VACC data for a national cohort of VHA enrollees. We will identify frequency of use of 26 low-value services in 6 categories: cancer screening, diagnostic/preventive testing, preoperative testing, imaging, cardiovascular testing/procedures, and surgery. We will apply average HERC cost estimates to calculate total costs of each service and category in VAMCs and in VACC. We will use multilevel modeling to examine facility variation in rates of VAMC and VACC low-value service use and extent to which Veteran and VAMC factors explain this variation. Aim 2 will involve similar analyses involving VA utilization data and Medicare claims for dual VA-Medicare enrollees. Aim 3 will apply latent profile analysis to facility-level estimates of low-value service categories to identify clusters of VAMCs with similar patterns of low-value service use in VA and non-VA settings. We will conduct interviews with VA providers who practice at VAMCs in different clusters to examine barriers and facilitators to de- implementing low-value services for Veterans. Next Steps & Implementation: We will use results to work with operations partners to develop performance measures, policies, and interventions to mitigate Veterans? receipt of low-value care in VA and non-VA settings, as VA evolves as a provider and payer of Veteran care.